Not all Detroit Diesels have turbo's. The turbo was added for more performance. The reason that they have a blower is because without one you would never get it to start. You need the air to be forced into the airboxes in order for the engine to have enough air for full combustion. And since a turbo doesn't make boost pressure until you have heat energy(exhaust) built up, you need to use a blower to supply that air at low rpm's. Detroit diesels come in many sizes, actually you can make a 16 cylinder by bolting two engines together, there is probably more to it than that but I know it can be done. I work for the railroad, and we have some 16 cylinder EMD's made by GM, that are are over 11,300 cu.inches, and these things have very unique turbo's, when the engine is anywhere from idle through about 3/4 throttle, the turbo is gear driven by a large clutch pack which is meshing with the gear train. After 3/4 throttle, the turbo comes off the clutch and the exhaust pressure takes over driving the turbo at full rpm's.